In the foregoing discussion we have alluded to various incomplete studies and opportunities for further research. In this section, we shall list some open research issues related to QoS scheduling in WiMAX, viz.,
§ An open issue is to how to provide tight delay and throughput guarantees in rtPS and ertPS traffic classes while using round robin schedulers, i.e., WRR and DRR. Also, the applications of other variations of round robin, such as smoothed round robin and stratified round robin, need to be further investigated.
§ Integration of time-stamped schedulers, such as WF2Q, SCFQ, and SFQ, with IWFQ type of algorithms for wireless networks, thus designing schedulers that are specific for high priority traffic classes of WiMAX.
§ The use of IWFQ within rtPS and ertPS traffic classes needs to be investigated further, as it requires significant support from the MAC layer.
§ The CIF-Q algorithm has higher complexity, and authors have argued that the wireless part has a lower bandwidth, which is obviously not true in the case of WiMAX. Thus, an interesting area for further work is to investigate the behavior of CIF-Q with rtPS and ertPS traffic classes.
§ Design of dynamic and efficient priority-based mechanisms for distribution of the allocated grants among the various classes at SS. The issues of inter- and intraclass fairness need to be investigated further.
§ Development of intelligent bandwidth requests, admission control, and bandwidth allocation schemes at the BS. Also, an investigation of efficient and adaptive techniques for traffic policing and shaping at BS/SSs is required.
§ It is important to investigate the use of RED-based buffer management for BE at SSs. Also, the use of modern scheduling techniques, such as multiuser diversity, that exploit variations in wireless channels must be investigated. Similarly, cross-layer approach, adaptive bandwidth requests, and queue length based scheduling are needed to be investigated further. One of the basic issues with the cross-layer approach is how to cater for multiple SSs in the same time frame.
§ Performance measurements of WiMAX based services is also very important. For this purpose a test bed has been developed, which employs the well-known Packet-E-Model for estimation of voice quality. It is also important to develop models that can estimate performance of various services (voice/video/data) offered in WiMAX. Hence, this area also needs to be investigated further.
§ One of the important issues is cooperation between various current technologies, for the benefit of customers. In this regard, the interoperation WiMAX with 3GPP’s High Speed Packet Access based technologies would be very worthwhile to investigate.
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